Understanding Linear Dimensions

By Carry‑On Checker Editorial •

In one line: Some airlines use a single limit for your bag’s linear dimensions — the sum of its L + W + H.

What are linear dimensions?

Linear dimensions are the sum of your bag’s Length, Width, and Height. Instead of three separate maximums, the airline publishes one number that your total must not exceed.

Formula: Linear = L + W + H

How to measure correctly

Measure external size (include wheels and handles).
Record each side to the widest/thickest point.
Add the three numbers. If your total is less than or equal to the airline’s limit, you’re within policy.

Typical reference limits

Bag type	Common linear max (U.S.)	Common linear max (International)
Carry‑on	≈ 45 in	≈ 115 cm
Checked (for context)	≈ 62 in	≈ 158 cm

These figures are common references—always check your airline’s exact limits.

Worked examples

Example A (inches): Bag is 21 × 14 × 9 in → Linear = 21 + 14 + 9 = 44 in → typically within a 45‑inch carry‑on limit.
Example B (centimeters): Bag is 55 × 36 × 23 cm → Linear = 55 + 36 + 23 = 114 cm → typically within a 115‑cm limit.

Borderline? Aircraft bins and sizers vary. If you’re within 1–2 cm (or 0.5") of the limit, consider downsizing or packing lighter to avoid gate‑check surprises.

How this relates to the checker

When an airline posts a linear maximum instead of three separate dimensions, the checker compares your sum against that limit. You’ll see a likely OK when your total is ≤ the limit and a may not fit warning when it exceeds it.

Check your airline’s policy Open the Carry‑On Checker

FAQs

Do wheels and handles count? Yes—use external dimensions unless your airline explicitly says otherwise.

Can a bag pass linear limits but fail individual side limits? Yes. Some airlines use either method; always compare against the rule your airline actually publishes.

Questions or corrections? Email .